Polyglycolic acid (PGA, including polyglycolide) has biodegratability and is also excellent in heat resistance, gas barrier property, rigidity (as a mechanical property for use as a packaging material), etc., so that the development of new use thereof as forming materials, such as various sheets, films and injection molding products has been envisaged (JP-A 10-60136, JP-A 10-80990, JP-A 10-138371, JP-A 10-337772). However, as polyglycolic acid resin has hydrolyzability, a composite forming material having improved properties together with another thermoplastic resin material is desired rather than the use thereof alone as a forming material.
On the other hand, aromatic polyester resins which are polycondensate products of aromatic dicarboxylic acids represented by (tere)phthalic acid and diols are excellent in transparency, rigidity and easy formability, and so-called “PET bottles” including polyethylene terephthalate that is a representative thereof as a representative material name are widely used as beverage bottles. Such a beverage bottle is required to have oxygen barrier property for preventing degradation of contents and carbon dioxide gas barrier property for preventing gasification of carbon dioxide dissolved under pressure in a foamable beverage so that an improved gas barrier property is desired.
Accordingly, several trials have been made to obtain a forming material using polyglycolic acid resin and excellent in mechanical properties and gas barrier property required of a packaging material, particularly a composite material suitable as a packaging or container-forming material, by compositing polyglycolic acid resin as described above with aromatic polyester resin by mixing or lamination.
For example, U.S. Pat. No. 4,424,242 to Barbee discloses a multilayer packaging material comprising a press-formed laminate of a polyglycolic acid film and a polyester terephthalate film. Further, U.S. Pat. No. 4,565,851 to Barbee discloses a polymer blend comprising polyglycolic acid and aromatic polyester resin in a weight-basis blend ratio of 50/50–5/95.
However, of the above-mentioned composite materials, the laminate is poor in melt processing characteristic and stretching property. On the other hand, as for the polymer blend, a material containing polyglycolic acid in excess of 25 wt. % is excluded from an object for evaluation by stretching. Further, both composite materials contain aromatic polyester resin as a major resin component and aim at improving the gas barrier property thereof with a relatively minor amount of polyglycolic acid resin, and therefore it is difficult to regard them as a material fully utilizing excellent properties of polyglycolic acid resin.